1. Field of the Invention
The invention relates to an application for low current consumption, and more particularly to a method for power-on sequence and a device with low current power source.
2. Related Art
With the progress of the technology, the electronic technology has been progressed from the earliest vacuum tube and transistor to the integrated circuit chip, which has the quite wide applications. Thus, the electronic products have gradually become the indispensable essentials in the life of the modern human beings. Today, the global environment was severely damaged. More and more People concern about the environmental protection, and more products around us gradually began to move closer to the environmental protection. The electrical product with solar cell is widely adopted by people, such as solar calculator, LED lamp with solar power and so on.
FIG. 1 illustrates a circuit block diagram depicting a solar-powered product according to the conventional art. Referring to FIG. 1, the product includes a solar cell 101, a capacitor 102, a reset circuit 103, an enable circuit 104 and a multi-functional block 105. Generally speaking, when the solar cell 101 receives the sun light, the charges would store in the capacitor 102. When the voltage of the capacitor 102 is greater than a threshold voltage VT, the reset circuit 103 would perform power-on reset (FOR). In addition, the enable circuit 104 would enable the multi-functional block 105 to start the solar-powered product up.
FIG. 2 illustrates a waveform diagram depicting the operation of the solar-powered product in FIG. 1 according to the conventional art. Referring to FIG. 2, when the power-on reset signal LVRB converts from the logic low voltage to the logic high voltage, every function block 105 would be started up at the same time. However, some function blocks 105 require higher start-up current, such as charge pump, voltage regulator, etc. Moreover, for the application in low power consumption, such as product with solar lower than 50 lux, the solar cell 101 only can provide a constant current about 5 uA. The power voltage VDD may drops too quick because of the great current consumption according to the operation of the function blocks at the same time, such that the low voltage reset is triggered. Meanwhile, the function blocks are disabled. When the voltage again is greater than the threshold voltage VT, the power-on reset signal LVRB converts from the logic low voltage to the logic high voltage again. Then, every function block 105 would be started up at the same time. And, it causes that the low voltage reset is triggered because of the high voltage drop of the power voltage VDD. Therefore, the solar-powered product would be lockout as the abovementioned cycle.
In order to solve the abovementioned issue, the engineer would greatly increase the capacitance of the capacitor 102, such as 20 uF. Although, the abovementioned cycle may be solved, the start-up time would be too long (about 10 seconds) since the current supplying capability is only 5 uA. End user would hardly accept long start-up time of the solar-powered product.